Abstract
Eighteen pan lysimeters were installed at a depth of 1.2 m in a Hagerstown silt loam soil in a corn field in central Pennsylvania in 1988. In 1995, wick lysimeters were also installed at 1.2 m depth in the same access pits. Treatments have included N fertilizer rates, use of manure, crop rotation (continuous corn, corn-soybean, alfalfa-corn), and tillage (chisel plow-disk, no-till). The leachate data were used to evaluate a number of nitrate leaching models. Some of the highlights of the 11 years of results include the following: 1) growing corn without organic N inputs at the economic optimum N rate (EON) resulted in NO3-N concentrations of 15 to 20 mg l in leachate; 2) use of manure or previous alfalfa crop as partial source of N also resulted in 15 to 20 mg l of NO3-N in leachate below corn at EON; 3) NO3-N concentration in leachate below alfalfa was approximately 4 mg l; 4) NO3-N concentration in leachate below soybeans following corn was influenced by fertilizer N rate applied to corn; 5) the mass of NO3-N leached below corn at the EON rate averaged 90 kg N ha (approx. 40% of fertilizer N applied at EON); 6) wick lysimeters collected approximately 100% of leachate vs. 40–50% collected by pan lysimeters. Coefficients of variation of the collected leachate volumes for both lysimeter types were similar; 7) tillage did not markedly affect nitrate leaching losses; 8) tested leaching models could accurately predict leachate volumes and could be calibrated to match nitrate leaching losses in calibration years, but only one model (SOILN) accurately predicted nitrate leaching losses in the majority of validation treatment years. Apparent problems with tested models: there was difficulty estimating sizes of organic N pools and their transformation rates, and the models either did not include a macropore flow component or did not handle macropore flow well.
Highlights
Nitrate in leachate from agricultural fields has been a serious pollutant of the nations waters for the last several decades
NO3–-N leached below corn at the economic optimum N rate (EON) rate averaged 90 kg N ha–1; 6) wick lysimeters collected approximately 100% of leachate vs. 40–50% collected by pan lysimeters
Concentrations in leachate from corn receiving the economic optimum N rate were always in the range of 14 to 21 mg l1, agree with those of similar studies using other means to estimate nitrate concentrations in leachate from optimally fertilized corn[8,9,10,11]. This relative uniformity of results appears to confirm that fertilizing corn at the economic optimum N rate will result in NO3-N concentrations in leachate that are 3 to mg l1 higher than the USEPA drinking water standard of mg NO3-N l1
Summary
Nitrate in leachate from agricultural fields has been a serious pollutant of the nations waters for the last several decades. According to Swistock et al.[1], more than half of the private wells in southeastern Pennsylvania, the main agricultural area in the state, have nitrate-N concentrations above the USEPA maximum contaminant level for drinking water of 10 mg l1 NO3-N. More recently it was concluded that the hypoxic zone in the Gulf of Mexico at the mouth of the Mississippi is mainly due to nitrates entering the river from agricultural fields[2] In spite of this concern with nitrate pollution from agricultural fields, few data are available showing the concentration and mass of nitrate that is leaching below agricultural fields in the Northeast and Mid-Atlantic regions of the U.S.; data on how these amounts are affected by crop rotation, N fertilizer rate, or tillage are lacking as well. Such data are needed to calibrate and test models of nitrate leaching in agricultural fields
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